Patent GB-1449610-A (GB)
Title: Electric circuits particularly for automatic battery charging apparatus
IPC: H02J7/10
Filed: 1972-12-29
Abstract: 1449610 Battery charging ELECTRIC POWER STORAGE Ltd 18 Dec 1973 [29 Dec 1972] 60062/72 Heading H2H Automatic battery charging equipment interrupts the charging current for periods (opencircuit intervals) during which the battery voltage drops to a predetermined level and terminates the main charging mode when the ratio of the duration of one open-circuit interval to the preceding open-circuit interval is below a predetermined interval for more than one such pair of intervals. The intervals are compared by supplying pulses to a counter at one frequency and a slightly lower frequency respectively during successive open circuit intervals and terminating the main charge if the number in the second interval falls short of that in the first interval. Charging current is supplied from A.C. source 42 via contact 40A, transformer 44 and bridge rectifier 46 to battery 26. The battery is connected to a voltage comparator having two different thresholds and also supplies power to most of the timing and control circuits. When a discharged battery is connected, the comparator, which has a lower threshold corresponding to a charged cell (2À3V) generates a low output which enables gate 36 allowing clock pulses (2Hz) to pass from master oscillator 30 to counter 32 and also switching relay 50 to close supply contacts 50A and thus actuate contactor 40. At a count of 2048, counter 32 generates a negative pulse which forces the comparator output to high and thus sets it to the lower threshold. The "high pulse" is shorter than the response time of the switching circuit and relay 50 is not de-energized if the battery voltage is still below the lower threshold. Counter 33 fed from counter 32 has alternate states "odd' and "even" in successive feedings of counter 32 and controls the up/down counting respectively of "open-circuit" counter 60. When the battery voltage reaches 2À3V per cell, a 1 at the comparator output closes gate 36 de-energizes relay 50 via gate 62 and directs the master oscillator pulses to the open circuit counter 60. At the same time, counter 33 controls the direction of the count in 60 and via line 35 increases the oscillator frequency by 5%. Assuming the count is an up count, this continues until the battery voltage drops below 2À3V per cell and the comparator output goes low and the comparator simultaneously switches to the higher threshold. The next charging period lasts for 2048 normal pulses and is terminated when a pulse via capacitor 34 switches the comparator to its low threshold a high output. Counter 33 has stepped and directs counter 60 to count down, the count terminating normally at zero. When the counter 60 output fails to reach zero on the down count before the comparator responds, the fully charged condition is satisfied and a pulse is sent to counter 80. After two such pulses counter 81 changes state and switches the system to a different phase in which the charging period is shortened by a factor of 8 (increasing the oscillator frequency by line 83). Lamps 90 and 91 responding to the state of counter 81, indicate the main charging or "topping-up" phase. A voltage doubler comprising diode 202, capacitor 200 and resistor 204 provides a switching off signal if the battery is removed. Means are also provided to switch on to the top-up phase should the counter 60 be filled due to a failure elsewhere in the circuitry.